The present invention relates to subterranean cementing operations, and more particularly, to methods of cementing in subterranean formations using cement compositions that autogenously cure voids that may form in such cement compositions.
Hydraulic cement compositions are commonly used in subterranean operations, particularly subterranean well completion and remedial operations. For example, hydraulic cement compositions are used in primary cementing operations whereby pipe strings, such as casings and liners, are cemented in well bores. In performing primary cementing, hydraulic cement compositions are pumped into the annular space between the walls of a well bore and the exterior surface of the pipe string disposed therein. The cement composition is permitted to set in the annular space, thereby forming an annular sheath of hardened, substantially impermeable cement therein that substantially supports and positions the pipe string in the well bore and bonds the exterior surfaces of the pipe string to the walls of the well bore. Hydraulic cement compositions also are used in remedial cementing operations such as plugging highly permeable zones or fractures in well bores, plugging cracks and holes in pipe strings, and the like.
Once the cement sets, voids may be present in the resultant set cement sheath. These voids may result from a number of possible causes, such as from the occurrence of a chemical reaction during hydration, from stresses imparted onto the cement composition caused by subterranean operations, and/or from stress exerted by the environment. For example, where hydration occurs too rapidly, voids may result. Voids may form from pipe movements, pipe expansions, impacts, and/or shocks generated by drilling and other subterranean operations, that may occur simultaneously with the setting of the composition. In one instance, voids may form during subterranean operations from the use of expandable tubulars, such as pipes, pipe strings, casings, liners, and the like.
Voids in set cement sheaths are generally undesirable, inter alia, because they may lead to loss of zonal isolation, which may allow formation fluids to enter the well bore and/or well bore fluids to enter the formation. In an attempt to counteract this problem, various additives (e.g., fibers and/or expansion additives) have been added to cement compositions. However, such techniques may not prevent the formation of voids and thus can lead to a loss of zonal isolation.